template <typename T> T f(int) { return T(); }
template <typename U, typename T, typename V> T f(V);

template int f<int> (int);

Here, the first f is more specialized than the second.  G++ currently rejects this testcase as ambiguous because of the unused template parameter U, but since DR 214 14.8.2.4 says,

In most cases, all template parameters must have values in order for deduction to succeed, but for partial ordering purposes a template parameter may remain without a value provided it is not used in the types being used for partial ordering.

clang and EDG get this right.

I noticed this issue while looking at bug 22596.